Faraday Discussions最新文献

The copolymerization of β-myrcene (M) with ethylene (E) and isoprene (I) was successfully promoted by a dichloro{1,4-dithiabutanediyl-2,2′-bis(4,6-di-alkylphenoxy)}titanium complex (1) activated by methylaluminoxane (MAO). The catalytic system afforded well-defined PME copolymers and novel PMEI terpolymers with controlled compositions (up to 49% of terpene incorporated in the case of PME). Microstructural analysis demonstrated high stereoselectivity of 1, with 1,4-trans insertion predominating for both isoprene (97%) and myrcene (94%). A comprehensive analysis by ¹³C and 2D NMR techniques confirmed a multi-block architecture for the novel synthesized copolymers. Notably, PMEI terpolymers exhibited a strong tendency toward forming alternating ethylene–isoprene (E–I) sequences. The thin film morphology, investigated by tapping mode atomic force microscopy (AFM), for the PME and PMEI copolymers, evidenced a phase-separated morphology consisting of soft and hard phases, respectively, ascribed to polydienic and polyethylenic domains. The materials displayed glass transition temperatures ranging from −62 to −74 °C, demonstrating their potential as sustainable and high-performance elastomers.

Sitka Spruce (SiS) dominates wood production in Scotland and represents an important source of wood in the UK. A systematic analysis of the lignin obtained from SiS sawdust using methano-, ethano-, butano- and isobutano-solv pretreatments was carried out. Detailed analysis of the resulting lignin using a range of methods (GPC, ³¹P after phosphitylation and HSQC NMR) and assessment of solvent costs enabled a comparison of the 4 pretreatment methods. The high quality of the lignin obtained reflects its stabilisation through alcohol incorporation at the α-position of the β-O-4 units. Scale up of the butanosolv pretreatment led to the controlled synthesis of a selectively oxidised form of the lignin (SiS lignin^OX) on a relatively large scale. Additional insights into the detailed structure of lignin^OX are presented. It is argued that this interesting, modified biopolymer may have significant potential for enhanced lignin valorisation.

Lignin is one of the main byproducts of the pulp, paper, and cellulosic ethanol industries. For the past 35 years, it has received increased interest in applications other than its use as an energy source. Although much of this research requires the use of lignin solubilized in solvents such as alkalis, little is known about the impact of the main process conditions – initial lignin mass, alkali concentration, and temperature and time of dissolution – on key solution properties – density, mass fraction of lignin, and pH. A central composite design, with these process conditions as input variables and these key solution properties as output variables, was made by varying the temperature from 30 to 80 °C, the time from 1 to 3 h, the concentration from 0.1 to 0.5 M, and, instead of directly working with lignin mass, a ratio of added lignin to alkali concentration of 30 to 60 g L mol⁻¹. The hypothesis made by Sarkanen et al. (Macromolecules, 1984, 17(12), 2588–2597) that lignin may aggregate under strong alkaline media and Lindströmn's (Colloid Polym. Sci., 1979, 257, 277–285) hypothesis that there are thermally induced processes that also cause aggregation – and further agglomeration – were attested and updated to indicate a joint action of both factors. Surprisingly, mass fraction displayed a maximum value using fixed ratio conditions instead of a saturation point. That shows lignin solubilization depends on more factors than simply the ratio of hydroxide anions vs. phenolic-OH groups and the pH. pH evolution was governed by slow aggregation and agglomeration reactions and conformational changes sensitive to time and temperature. The resulting polynomial models achieved adjusted R² > 0.996 for all responses, and ten validation experiments exhibited maximum relative errors ≤1.6%. These results furnish quantitative guidelines for tailoring lignin solution properties and suggest further studies into rheology, extended factor ranges, alternative lignin sources, and developing theoretical – and possibly more universal – models to predict lignin solution properties.

Lignin–carbohydrate complexes, in which lignin and polysaccharides are directly connected, have been identified and extensively analyzed. To date, however, the origin of these structures has not been unequivocally established. That notwithstanding, it has been found that delignification, whether by conventional pulping and bleaching processes or in the biorefinery context, is effected by the presence of lignin–carbohydrate complexes. Using density functional theory calculations, the current work has evaluated the thermodynamics of bond dissociation as a function of structure and chemical composition. Among the lignin–carbohydrate complexes that have been identified, the homolytic bond dissociation energy is highest for the α-benzyl ethers and γ-ester, with phenyl glycosides being markedly less endothermic. This is consistent with observations on the recalcitrance of these compounds. Heterolytic cleavage reactions of the α-benzyl ethers are less endothermic, due to water solvation of the ions. The latter observation may provide support for the proposed homolytic cleavage reaction, since if heterolysis were operative, the α-benzyl ethers would not exhibit the level of recalcitrance that is observed experimentally.

Electrocatalysis is critical for mitigating climate change by providing green energy solutions, e.g. for hydrogen production by electrolysis of water implying high catalytic activity not only for hydrogen evolution but also for oxygen evolution as the counter reaction. Moreover, reactions such as oxygen reduction and nitrate reduction are of high importance in fuel cells or for environmental remediation. This study focuses on the exploration of electrocatalysts in the enormous composition spaces encountered in multinary materials like high-entropy alloys in the form of compositionally complex solid solutions. These provide paradigm-changing design principles for new electrocatalysts based on their tuneable surface atom arrangements resulting from their multinary composition. However, to master the combinatorial explosion problem of polyelemental catalysts, efficient exploration approaches need to be adapted. For this purpose, we present a comprehensive strategy to compare the electrocatalytic activity for different reactions in alkaline media, namely the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and nitrate reduction reaction (NO_xRR) over large compositional spaces in three multinary systems: Cu–Pd–Pt–Ru, Ir–Pd–Pt–Ru and Ni–Pd–Pt–Ru. To generate the necessary large and multidimensional experimental dataset, thin-film materials libraries were synthesised and analysed using high-throughput characterisation methods. This allows for a comparative overview over correlations between composition and electrocatalytic activity, considering also relevant information on crystal structure and surface morphology. Similarities and differences, trends, maxima and minima in electrocatalytic activity are revealed and discussed. Main findings include that for the OER Ir₂₃Pd₃Pt₈Ru₆₆ exhibits the highest activity, exceeding any alloy of the other two systems by 51% (Ni–Pd–Pt–Ru) and 74% (Cu–Pd–Pt–Ru). For HER, Ir₃₆Pd₄Pt₄₈Ru₁₂ surpasses any of its elemental constituents by 26% and maxima in other systems by 5% (Ni–Pd–Pt–Ru) and 23% (Cu–Pd–Pt–Ru). For the NO_xRR, only a marginal increase of 4% was found between the most active measured alloy and the elemental constituent Cu. By comparing activity across systems, we demonstrate the tunability of electrochemical activity on compositionally complex solid solutions, achievable through variations in composition both within and across different material systems for four different reactions.

Reversible addition–fragmentation chain-transfer (RAFT) depolymerization offers a promising and (comparatively) low-temperature chemical recycling strategy, enabling high yields of recovery of monomers. Conducting this process under continuous flow conditions, in combination with an inline dialysis set-up was recently demonstrated to accelerate depolymerization. However, several kinetic aspects of the process remain poorly understood, complicating the optimization of flow processes. In this study, we determined the kinetics of RAFT depolymerization under continuous flow conditions on the example of poly(butyl methacrylate), polyBMA. Depolymerizations were followed at temperatures from 120 °C to 160 °C, and the activation energy of the process was determined to be 79.5 kJ mol⁻¹. Further, a square root dependence of the rate on the initial polymer concentration was determined. Comparison of the rates of depolymerization with clearance rates during in-flow membrane dialysis showed that the dialysis process is, by a large margin, the rate-determining step in the entire process. Removal of monomer was accelerated by increasing the cross-flow rate in the dialysis, providing a first step towards optimal conditions in the flow depolymerization.

Biomineralisation integrates complex biologically assisted physico-chemical processes leading to an extraordinary diversity of calcareous biomineral crystalline architectures, in intriguing contrast with the consistent presence of a submicrometric granular structure. While the repeated observation of amorphous calcium carbonate is interpreted as a precursor to the crystalline phase, the crystalline transition mechanisms are poorly understood. Access to the crystalline architecture at the mesoscale, i.e., over a few granules, is key to building realistic crystallisation models. Here we exploit three-dimensional X-ray Bragg ptychography microscopy to provide a series of nanoscale maps of the crystalline structure within the “single-crystalline” prism of the prismatic layer of a Pinctada margaritifera shell. The mesocrystalline organisation exhibits several micrometre-sized iso-oriented/iso-strained crystalline domains, the detailed studies of which reveal the presence of crystalline coherence domains ranging from 130 to 550 nm in size. The further increase in the lattice parameter with the size of the coherence domain likely results from the crystallisation mechanism, pointing towards a maturation process occurring after the initial amorphous-to-crystalline transition.

Recent progress in circular 3D-printable photocurable resins that enable closed-loop recycling marks a significant step forward in reducing wasteful manufacturing methods and non-recyclable printed plastics. However, with 3D printing technologies shifting from prototyping to full-scale production, the demand for high-scale processes and easily tuneable resin compositions can benefit from the design of automated systems. Herein, we report on the on-demand preparation of a circular 3D-printable resin, achieved through a continuous flow approach. A supported enzyme (Lipase B from Candida antarctica) was used to promote a green esterification of the lipoic acid with biobased alcohols to prepare circular biobased photocurable resins. The supported enzyme was employed for the preparation of a packed bed reactor and was easily recycled and reused to achieve the continuous production of lipoate-based photocurable resins with tuneable composition. Lastly, the environmental impact of the developed on-demand manufacturing process was compared to the previously reported esterification protocols through life cycle assessment, showing the effectiveness of continuous enzymatic flow synthesis in enhancing environmental performance across multiple areas, from human health to ecosystem impact and resources.